Polyimide film comprising at least two fillers having different diameters, and electronic device comprising same

ABSTRACT

The present invention provides a polyimide film comprising an inorganic filler, which comprises a first filler group having a diameter (D50) of 2-2.7 μm and a second filler group having an average diameter (D50) of 1-1.7 μm, wherein the polyimide film satisfies relation 1: 0.7≤(D90−D10)/(D50)≤1.2, which is about the respective diameters of the first filler group and the second filler group.

TECHNICAL FIELD

The present disclosure relates to a polyimide film including two or morefillers having different particle diameters, and an electronic deviceincluding the same.

BACKGROUND ART

Polyimide (PI) is a polymer material that is based on a rigid aromaticbackbone and an imide ring with very excellent chemical stability tohave the highest level of heat resistance, chemical resistance,electrical insulation, and chemical resistance among organic materials.

Thus, the polyimide has been widely used as a core material inautomobiles, aerospace fields, and flexible circuit boards, etc.Recently, in accordance with the development of a colorless andtransparent polyimide film, the polyimide has also been used for aninsulation and protective film of a display requiring opticalproperties, flexibility resistance, abrasion resistance, dimensionalstability, etc.

The polyimide film may be manufactured by preparing a polyamic acidsolution, which is a precursor, forming a film at a small thicknessusing the polyamic acid solution, and then performing heat-treatment.

The polyimide film thus manufactured may be processed with a nip-roll,etc., for improving smoothness, or may be corona-treated for surfacemodification, and may be wound by a roll and stored.

However, since a general polyimide film has a low average roughness,when the polyimide film is finished as described above, a blockingphenomenon may be caused on a surface of the polyimide film, and thereis a limitation in a process that it is not easy to wind the polyimidefilm.

For this reason, a method of improving an average roughness andminimizing the blocking phenomenon of the polyimide film by addingfillers such as titanium oxide, alumina, silicon nitride, boron nitride,calcium hydrogen phosphate, calcium phosphate, mica, etc., to thepolyamic acid solution, which is the precursor of the polyimide film,has been considered.

However, the inorganic fillers described above are not excellent incompatibility with the polyamic acid solution, which is the precursor ofthe polyimide, and thus have poor dispersibility. In addition, theinorganic fillers are generally atypical in that particle forms are notconstant, have a large specific surface area, and have a feature that itis easy for particles of complementary forms to be bonded to each other.

Thus, the inorganic fillers are not easily dispersed in the polyamicacid solution, and may be agglomerated.

The aggregated inorganic fillers may form large and small protrusions onthe surface of the polyimide film, thereby reducing smoothness,transmittance, etc., of the polyimide film. In addition, the protrusionsmay damage a surface of an object to or with which the polyimide film isadhered or is in contact, for example, a display.

The protrusions cause light scattering as well as a decrease intransparency and transmittance in the polyimide film, and may thus actas a fatal disadvantage for the polyimide film for the display in whichexcellent optical properties are essentially required.

Thus, there is a high need for a novel polyimide film that may solvesuch a problem at once.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a polyimide filmhaving no surface defects such as protrusions, having predeterminedaverage roughness and smoothness, and having excellent transmittance.

In one aspect of the present disclosure, inorganic fillers including aplurality of filler groups having an average particle diameter (D50)each falling within a specific range are disclosed as an essentialfactor for achieving the above object.

In particular, the plurality of filler groups may satisfy a specificrelational expression 1 of the present disclosure. In this specificcase, the inorganic fillers may be uniformly dispersed in a base film,and agglomeration of the inorganic fillers may thus be minimized.

As a result, even though the polyimide film of the present disclosureincludes fillers, protrusions due to aggregation of the fillers may notbe substantially generated.

The polyimide film may also have a predetermined average roughness,smoothness, and excellent transmittance because the inorganic fillersinclude filler groups of which average particle diameters fall withindifferent ranges, and may be applied to technical fields such as adisplay on the basis of such a fact.

In another aspect of the present disclosure, the polyimide film may havea predetermined modulus suitable for an electronic device whose shape isvariably deformed, such as a display device.

Therefore, a substantial object of the present disclosure is to providespecific embodiments of the present disclosure.

Technical Solution

In one embodiment, the present disclosure provides a polyimide filmincluding: a base film made of polyimide, and inorganic fillersdispersed in the base film,

wherein the polyimide film has a modulus of 3.5 GPa or less,

the inorganic fillers include a first filler group having an averageparticle diameter (D50) falling within the range of 2 μm to 2.7 μm and asecond filler group having an average particle diameter (D50) fallingwithin the range of 1 μm to 1.7 μm, and

each of the first filler group and the second filler group satisfies thefollowing relational expression 1 for particle diameters.

In one embodiment, the present disclosure provides a method ofmanufacturing a polyimide film.

In one embodiment, the present disclosure provides an electronic deviceincluding a polyimide film as at least one of an optical film, aninsulating film, and a protective film.

The electronic device may be a display device or a wearable instrumentwhose shape is variably deformed through at least one selected frombending, curving, and rolling, and the polyimide film may be deformedtogether in response to the deformation of the electronic device.

Hereinafter, embodiments of the present disclosure will be described inmore detail in the order of a “polyimide film” and a “method ofmanufacturing the polyimide film” according to the present disclosure.

Terms and words used in the present specification and claims are not tobe construed as a general or dictionary meaning, but are to be construedas meaning and concepts meeting the technical ideas of the presentdisclosure based on a principle that the present inventors mayappropriately define the concepts of terms in order to describe theirinventions in the best mode.

Therefore, the configurations of embodiments described in the presentspecification are only one of the most preferred embodiments of thepresent disclosure and do not represent all the technical spirits of thepresent disclosure. Thus, it should be understood that there may bevarious equivalents and modification examples that can replace them atthe time of filing the present application.

Singular forms as used herein include plural forms unless the contextclearly indicates otherwise. It should be understood that the term“comprise,” “includes,” or “have,” etc., as used herein specifies thepresence of implemented features, numerals, steps, components, or acombination thereof, but does not preclude the presence or addition ofone or more other features, numerals, steps, components, or acombination thereof.

The term “dianhydride” as used herein is intended to include a precursoror derivative thereof, which may not technically be a dianhydride, butnevertheless will react with diamine to form a polyamic acid, and thepolyamic acid may be again converted into the polyimide.

The term “diamine” as used herein is intended to include a precursor orderivative thereof, which may not technically be diamine, butnevertheless will react with a dianhydride to form a polyamic acid, andthe polyamic acid may be again converted into the polyimide.

It should be understood that when an amount, concentration, or othervalue or parameter as used herein is given as an enumeration of a range,a preferable range, or preferable upper and lower values, all rangesformed with any upper limit or preferable values of any one pair and anylower limit or preferable values of any one pair are specificallydisclosed, regardless of whether the range is disclosed separately. Whena range of numerical values is referred to herein, the range is intendedto include endpoints thereof and all integers and fractions within thatrange, unless stated otherwise. It is intended that the scope of thepresent disclosure is not limited to specific values recited when therange is defined.

Polyimide Film

A polyimide film according to the present disclosure may include a basefilm made of polyimide, and inorganic fillers dispersed in the basefilm.

Here, the inorganic fillers may include a first filler group having anaverage particle diameter (D50) falling within the range of 2 μm to 2.7μm and a second filler group having an average particle diameter (D50)falling within the range of 1 μm to 1.7 μm. Each of the first fillergroup and the second filler group may satisfy the following relationalexpression 1 for particle diameters:

0.7≤(D90−D10)/(D50)≤1.2  (1).

Even in the filler group having the same average particle diameter, aparticle diameter distribution may be different, and influences on aneffect may be different depending on the particle diameter distribution.Such particle diameter distribution may be confirmed by D10, D50, andD90.

D90 is a particle diameter of the smallest particle among 10% of theparticles having large particle diameters even in the filler group, D10is a particle diameter of the largest particle among 10% of particleshaving small particle diameter in the filler group, and the averageparticle diameter (D50) is a particle diameter of the largest particleamong 50% of particles having small particle diameters in the fillergroup.

A particle diameter deviation between the particles constituting thefiller group may be related to various factors, and a difference betweenD90 and D10 may also be considered as one of those factors.

In summary, it may be interpreted that the larger the difference betweenD90 and D10, the larger the particle diameter deviation between theparticles constituting the filler group, and it may be interpreted thatthe smaller the difference between D90 and D10, the smaller the particlediameter deviation between the particles constituting the filler group.

In this regard, when the inorganic fillers of a single filler group aredispersed in the base film, a large particle diameter deviation, thatis, out of the range of the above relational expression 1 means“non-uniform distribution of particles” in which there are more “largeparticles” having a particle diameter of about D90 in any one part ofthe base film, and there are more “small particles” having a particlediameter of about D10 in the other part of the base film.

The non-uniform distribution of inorganic fillers in the base film makesthe polyimide film have a non-uniform surface roughness, and largeparticles or small particles are biased to any one part of the basefilm, such that protrusions derived from the inorganic fillers may beformed on a surface of the polyimide film.

Therefore, it can be understood as a factor capable of suppressingprotrusion formation that the particle diameter variation of theparticles constituting the filler group is small.

Even though the particle diameter deviation is at an appropriate level,if the average particle diameter of the filler group is excessivelylarge, the number of particles settled by gravity in the polyamic acidsolution, which is a precursor of the base film, may be increased. Thus,the particles may be biased in one part of the base film, which isanother example of the non-uniform distribution of particles describedabove. In addition, a filler group having an excessive large averageparticle diameter may contribute to the improvement of the averageroughness of the polyimide film, but may reduce the smoothness andtransmittance of the film. In another aspect, in the case of a polyimidefilm for a display requiring high quality, the filler particlesthemselves having an excessively large particle diameter may also berecognized as defects.

In addition, even though the particle diameter deviation is at anappropriate level, if the average particle diameter of the filler groupis excessively small, the filler particles are likely to be aggregatedin the polyamic acid solution due to an increase in a specific surfacearea of the filler group, and accordingly, protrusion formation may becaused. In addition, a filler group having an excessively small averageparticle diameter may contribute to the improvement of smoothness andtransmittance, but may significantly reduce the average roughness, whichmay act as a cause of generating additional defects such as scratches ina manufacturing process of the film.

That is, it is difficult to solve the above-described problems witheither factor of the particle diameter deviation and the averageparticle diameter of the filler group.

Furthermore, if the average particle diameter is large, the differencebetween D90 and D10 may be large even thought the particle distributionis uniform, whereas if the average particle diameter is small, thedifference between D90 and D10 may be small even thought the particledistribution is non-uniform. Thus, there is a limit to representing theparticle diameter distribution only by the difference between D90 andD10.

Thus, the particle diameter distribution may be represented only when arelationship among D10, D50, and D90 is established as in the relationalexpression 1, and the desired effect of the present disclosure may beachieved only when the filler group satisfiers the range of relationalexpression 1.

It is assumed that dispersion efficiency of the particles constitutingthe filler group is increased, so that the particles may be distributedrelatively uniformly in the base film, when the filler group satisfiesthe relational expression 1. In fact, the polyimide film according tothe present disclosure may have substantially no protrusions or mayinclude a very small amount of protrusions, and may also have an averageroughness, smoothness and transmittance at appropriate levels. This willbe clearly demonstrated in ‘Best Mode’.

The polyimide film according to the present disclosure is alsocharacterized in that it has average roughness, smoothness, andtransmittance at appropriate levels by allowing features that may beexhibited from a first filler group and a second filler group tocomplementarily act through inorganic fillers including the first fillergroup and the second filler group whose average particle diameters fallwithin different ranges.

As described above, any one of the average roughness, the smoothness andthe transmittance of the polyimide film may be sacrificed according tothe average particle diameter of the filler group, and if a singlefiller group falling within one average particle diameter range is used,the average roughness, the smoothness and the transmittance will bedifficult to be compatible with each other.

However, the polyimide film according to the present disclosure is a newpolyimide film in which average roughness, and smoothness andtransmittance, which are difficult to be compatible with each other, arecompatible at a predetermined level, because an appropriate level ofaverage roughness may be maintained by the first filler group having arelatively large average particle diameter range, and the smoothness andthe transmittance may be inherent to an appropriate level by the secondfiller group having a relatively small average particle diameter range.

In one specific example of the above-mentioned features, the polyimidefilm has a haze of 12 or less, specifically 10 or less, and an averageroughness of 20 nm or more, specifically 20 nm to 50 nm, and morespecifically 20 nm to 40 nm. It can be expected that the transmittanceof the polyimide film according to the present disclosure is excellentbecause the haze is inversely proportional to the transmittanceSpecifically, the polyimide film according to the present disclosure mayhave a transmittance of 0.4 to 0.6 with respect to a relative value of 1which is a theoretical maximum transmittance.

In one specific example for implementing the above, the first fillergroup may have D90 of 3.0 μm to 4.1 μm and D10 of 1.0 μm to 1.6 μm, andthe second filler group may have D90 of 1.5 μm to 2.5 μm and D10 of 0.7μm to 1.2 μm.

If D90 of the first filler group is less than the above range, thespecific surface area based on the entire inorganic fillers may beincreased, thereby causing agglomeration of the particles, which is notpreferable. In addition, If D90 of the first filler group exceeds theabove range, the number of particles settled by gravity in the polyamicacid solution may be increased, which is not preferable.

If D10 of the first filler group is less than the above range, thespecific surface area based on the entire inorganic fillers may beincreased, thereby causing agglomeration of the particles, which is notpreferable. In addition, if D10 of the first filler group exceeds theabove range, a particle diameter deviation between particles of D10 ofthe first filter group and large particles of the second filler group,for example, particles of D90 may be large. In this case, thenon-uniform distribution of the inorganic fillers may be intensified,which is not preferable.

In addition, in a case of D90 and D10 of the second filler group,disadvantages similar to those of the first filler group described abovemay occur, and thus, it is preferable to select D90 and D10 in the aboveranges.

In one specific example for implementing the above-mentioned features,the polyimide film may include the inorganic fillers of 0.05% to 0.3% byweight, based on the total weight of the polyimide film.

If the content of the inorganic fillers exceeds the above range, themechanical properties of the polyimide film may be greatly decreased. Ifthe content of the inorganic fillers is less than the above range, theintended effect of the present disclosure may not be exhibited.

In addition, if the contents of the first filler group and the secondfiller group constituting the inorganic fillers are out of the scope ofthe present disclosure and are not compatible with each other, forexample, if the content of the second filler group is excessively high,and thus the content of the first filler group is decreased, the averageroughness may be decreased, but the smoothness and transmittance by thesecond filler group are not significantly improved.

Conversely, if the content of the first filler group is excessivelyhigh, and thus the content of the second filler group is decreased, theeffect of improving the smoothness and transmittance by the secondfiller group may not be exhibited, and non-uniform distribution may becaused.

That is, if the contents of the first filler group and the second fillergroup are at an appropriate level, the features that may be exhibited ineach of these groups are balanced, and the intended effect of thepresent disclosure may be expressed. However, if the contents of thefirst filler group and the second filler group are out of theabove-described appropriate level, the breakdown of this balance mayhave a negative impact on the polyimide film.

Thus, the present disclosure discloses the preferable contents of thefirst filler group and the second filler group.

In one example of the content, the inorganic fillers may include 60% to80% bye weight, specifically 65% to 75% by weight, and more specifically68% to 72% by weight of the first filler group, based on the totalweight of the inorganic fillers. The inorganic fillers may also include20% to 40% by weight, specifically 25% to 35% by weight, and morespecifically 28% to 32% by weight of the second filler group, based onthe total weight of the inorganic fillers.

It should be understood that the desired effect of the presentdisclosure may be exhibited when the first filler group and the secondfiller group selected within this content range are used.

Meanwhile, in some cases, for the purpose of improving the smoothness ofthe polyimide film, the inorganic fillers may further include a thirdfiller group having an average particle diameter (D50) falling withinthe range of 0.3 μm to 0.6 μm and satisfying the relational expression1.

However, since the third filler group has a small average particlediameter, such that it is easy for the particles of the third fillergroup to be aggregated and the average roughness of the polyimide filmmay be decreased, and it may thus be preferable that the third fillergroup is included in a limited amount. In one specific example of this,the inorganic fillers may include the third filler group in an amount of5% by weight or more to less than 20% by weight, specifically 5% to 10%by weight, and more specifically 7% to 10% by weight, based on the totalweight of the inorganic fillers.

When the inorganic fillers further includes the third filler group, apart of the second filler group may be included in a form in which athird filler group is replaced. In this case, a weight ratio of thethird filler group to the second filler group (the third filler groupweight/second filler group weight) may be 0.1 to 1.

The third filler group may have D90 of 0.4 μm to 0.9 μm and D10 of 0.2μm to 0.4 μm.

If D90 of the third filler group is less than the above range, thespecific surface area based on the entire inorganic fillers may beincreased, thereby causing agglomeration of particles, which is notpreferable. In addition, if D90 of the third filler group exceeds theabove range, it is difficult to expect improvement in smoothness.Further, if D10 of the third filler group is less than the above range,the specific surface area based on the entire inorganic fillers may beincreased, thereby causing agglomeration of particles. If D10 of thethird filler group exceeds the above range, it is difficult to expect animprovement in smoothness.

The inorganic fillers of the present disclosure may be one or moreselected from the group consisting of silica, calcium phosphate, calciumcarbonate, and barium sulfate having excellent compatibility with thepolyamic acid solution, and in detail, may be spherical silica havingpoor aggregation properties.

In one specific example, the polyimide forming the base film may bederived from imidization of a polyamic acid formed by the polymerizationof a dianhydride monomer and a diamine monomer.

The diamine monomer that may be used in the polymerization of thepolyamic acid is an aromatic diamine, and may be classified, forexample, as follows.

1) A diamine having one benzene ring on its structure and a relativelyrigid structure, such as 1,4-diaminobenzene (or paraphenylenediamine,PPD, PDA), 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene,3,5-diaminobenzoic acid (or DABA);

2) A diamine having two benzene rings on its structure, such asdiaminodiphenyl ether, for example, 4,4′-diaminodiphenyl ether (oroxydianiline, ODA) and 3,4′-diaminodiphenyl ether,4,4′-diaminodiphenylmethane (p-methylenedianiline),3,4′-diaminodiphenylmethane (m-methylenedianiline),3,3′-dimethyl-4,4′-diaminobiphenyl, 2,2′-dimethyl-4,4′-diaminobiphenyl,2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl,3,3′-dimethyl-4,4′-diaminodiphenylmethane,3,3′-dicarboxy-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane,bis(4-aminophenyl)sulfide, 4,4′-diaminobenzanilide,3,3′-dichlorobenzidine, 3,3′-dimethylbenzidine (or o-tolidine),2,2′-dimethylbenzidine (or m-tolidine), 3,3′-dimethoxybenzidine,2,2′-dimethoxybenzidine, 3,3′-diaminodiphenyl ether,3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether,3,3′-diaminodiphenylsulfide, 3,4′-diaminodiphenylsulfide,4,4′-diaminodiphenylsulfide, 3,3′-diaminodiphenylsulfone,3,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone,3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone,3,3′-diamino-4,4′-dichlorobenzophenone,3,3′-diamino-4,4′-dimethoxybenzophenone, 3,3′-diaminodiphenylmethane,3,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane,2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane,2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,3,3′-diaminodiphenylsulfoxide, 3,4′-diaminodiphenylsulfoxide,4,4′-diaminodiphenylsulfoxide;

3) A diamine having three benzene rings on its structure, such as1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene,1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-amino phenyl)benzene,1,3-bis(4-aminophenoxy)benzene (or TPE-R),1,4-bis(3-aminophenoxy)benzene (or TPE-Q),1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene,3,3′-diamino-4-(4-phenyl)phenoxybenzophenone,3,3′-diamino-4,4′-di(4-phenylphenoxy)benzophenone,1,3-bis(3-aminophenylsulfide)benzene,1,3-bis(4-aminophenylsulfide)benzene,1,4-bis(4-aminophenylsulfide)benzene,1,3-bis(3-aminophenylsulfone)benzene,1,3-bis(4-aminophenylsulfone)benzene,1,4-bis(4-aminophenylsulfone)benzene,1,3-bis[2-(4-aminophenyl)isopropyl]benzene,1,4-bis[2-(3-aminophenyl)isopropyl]benzene,1,4-bis[2-(4-aminophenyl)isopropyl]benzene;

4) A diamine having four benzene rings on its structure, such as3,3′-bis(3-aminophenoxy)biphenyl, 3,3′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl, 4,4′-bis(4-aminophenoxy)biphenyl,bis[3-(3-aminophenoxy)phenyl]ether, bis[3-(4-aminophenoxy)phenyl]ether,bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether,bis[3-(3-aminophenoxy)phenyl]ketone,bis[3-(4-aminophenoxy)phenyl]ketone,bis[4-(3-aminophenoxy)phenyl]ketone,bis[4-(4-aminophenoxy)phenyl]ketone,bis[3-(3-aminophenoxy)phenyl]sulfide,bis[3-(4-aminophenoxy)phenyl]sulfide,bis[4-(3-aminophenoxy)phenyl]sulfide,bis[4-(4-aminophenoxy)phenyl]sulfide,bis[3-(3-aminophenoxy)phenyl]sulfone,bis[3-(4-aminophenoxy)phenyl]sulfone,bis[4-(3-aminophenoxy)phenyl]sulfone,bis[4-(4-aminophenoxy)phenyl]sulfone,bis[3-(3-aminophenoxy)phenyl]methane,bis[3-(4-aminophenoxy)phenyl]methane,bis[4-(3-aminophenoxy)phenyl]methane,bis[4-(4-aminophenoxy)phenyl]methane,2,2-bis[3-(3-aminophenoxy)phenyl]propane,2,2-bis[3-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(3-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP),2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane.

The above-mentioned diamine may be used alone or in combination of twoor more as desired, but the diamine monomer that may be particularlypreferably used in the present disclosure may be one or more selectedfrom the group consisting of 4,4′-diaminodiphenyl ether (4,4′-ODA),3,4′-diaminodiphenyl ether (3,4′-ODA), p-methylenedianiline (p-MDA), orm-methylenedianiline (m-MDA) which is a monomer with characteristicscapable of improving transmittance.

The dianhydride monomer that may be used in the polymerization of thepolyamic acid may be an aromatic tetracarboxylic dianhydride.

Examples of the aromatic tetracarboxylic dianhydride includepyromellitic dianhydride (or PMDA), 3,3′,4,4′-biphenyltetracarboxylicdianhydride (or s-BPDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride(or a-BPDA), oxydiphthalic dianhydride (or ODPA),diphenylsulfone-3,4,3′,4′-tetracarboxylic dianhydride (or DSDA),bis(3,4-dicarboxyphenyl)sulfide dianhydride,2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,2,3,3′,4′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride (or BTDA),bis(3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimelitic monoester acid anhydride), p-biphenylenebis (trimeliticmonoester acid anhydride), m-terphenyl-3,4,3′,4′-tetracarboxylicdianhydride, p-terphenyl-3,4,3′,4′-tetracarboxylic dianhydride,1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride,1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride,1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride,2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),2,3,6,7-naphthalenetetracarboxylic acid dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,4,4′-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, etc. Theabove-mentioned aromatic tetracarboxylic dianhydride may be used aloneor in combination of two or more as desired, but the dianhydride monomerthat may be particularly preferably used in the present disclosure maybe pyromellitic dianhydride (PMDA).

Meanwhile, the polyimide film according to the present disclosure maysatisfy the following relational expression 2:

12 μm≤T*L≤40 μm  (2)

wherein, T is a thickness of the polyimide film and is 30 μm to 50 μm,and L is a transmittance of the polyimide film, is a relative value to 1which is a theoretical maximum transmittance, and is 0.4 to 0.8, andspecifically 0.4 to 0.6.

The polyimide film that satisfies these relationships may be suitable,for example, as an insulating or protective film of a display devicerequiring optical properties based on excellent light transmittance, indetail, a display device whose shape is variably deformed through atleast one selected from bending, curving, and rolling.

In one example, a display device of which both end portions aredeformed, for example, bent, in the same direction has an inner surfacefacing the direction in which the display device is deformed and anouter surface, which is a surface opposite to the inner surface. Whenthe display device is deformed, on the inner surface, force istransferred from both end portions of the display device toward acentral portion of the display device, and on the outer surface, forceis transferred from the central portion of the display device towardboth end portions of the display device.

If the polyimide film is added to an outer surface of the display devicedeformed as described above, a tensile force is formed on the polyimidefilm by force transferred from a central portion of the display devicetoward both end portions of the display device. Here, if the modulus ofthe polyimide film is excessively high, the polyimide film has brittleproperties and may not be deformed in a direction in which the polyimidefilm is tensioned. In this case, the polyimide film may apply stress tothe inside of the display to shorten a lifespan of the display.

Conversely, when the polyimide film is added to the inner surface, thepolyimide film tends to be compressed by the force transferred from bothend portions toward the central portion without forming separate tensileforce. Thus, it may be advantageous that the polyimide film added to theinner surface has a high modulus and has thus strong properties againstcompressive force.

The polyimide film according to the present disclosure has a modulus of3.5 GPa or less, and may be specialized in being added to the innersurface in a display device that is deformed based on a relatively lowmodulus. However, it is emphasized that the above mentioned is describedas a non-limiting example for the polyimide film according to thepresent disclosure, and the use of the polyimide film according to thepresent disclosure is not limited thereto.

Manufacturing Method of Polyimide Film

A method of manufacturing the polyimide film according to the presentdisclosure may include:

polymerizing a dianhydride monomer and a diamine monomer in an organicsolvent to prepare a polyamic acid solution;

mixing inorganic fillers with the polyamic acid solution to prepare aprecursor composition; and

forming a film on a support using the precursor composition andperforming imidization to form the polyimide film.

A method of polymerizing the polyamic acid includes, for example, thefollowing methods:

(1) a method of polymerizing the polyamic acid by adding the entireamount of a diamine monomer in an organic solvent, and then adding adianhydride monomer so that the dianhydride monomer and the diaminemonomer become substantially equimolar;

(2) a method of polymerizing the polyamic acid by adding the entireamount of a dianhydride monomer in an organic solvent, and then adding adiamine monomer so that the diamine minomer and the dianhydride monomerbecome substantially equimolar;

(3) a method of polymerizing the polyamic acid by adding some componentsof a diamine monomer in an organic solvent, mixing some components of adianhydride monomer to the reaction component in a ratio of about 95 mol% to 105 mol %, adding the remaining diamine monomer component andsubsequently adding the remaining dianhydride monomer component so thatthe diamine monomer and the dianhydride monomer become substantiallyequimolar;

(4) a method of polymerizing the polyamic acid by adding a dianhydridemonomer in an organic solvent, mixing some components of a diaminecompound to the reaction component in a ratio of about 95 mol % to 105mol %, adding the remaining dianhydride monomer component thereto andsubsequently adding the remaining diamine monomer component thereto sothat the diamine monomer and the dianhydride monomer becomesubstantially equimolar; and

(5) a method of polymerizing the polyamic acid by reacting some diaminemonomer components and some dianhydride monomer components in an organicsolvent such that any one of them is excessive to form a first polymer,reacting some diamine monomer components and some dianhydride monomercomponents in another organic solvent such that any one of them isexcessive to form a second polymer, and mixing the first and secondpolymers, wherein when the diamine monomer component is excessive whenforming the first polymer, the dianhydride monomer component isexcessive in the second polymer and when the dianhydride monomercomponent is excessive in the first polymer, the diamine monomercomponent is excessive in the second polymer so that the entire diaminemonomer component and the dianhydride monomer component used in thesereactions become substantially equimolar by mixing the first polymer andthe second polymer, and completing the polymerization.

However, the method is an example to aid in the practice of the presentdisclosure, the scope of the present disclosure is not limited thereto,and any known method may be used.

As the diamine monomer and dianhydride monomer, monomers as described inthe previous embodiment may be used.

The organic solvent is not particularly limited as long as it is asolvent in which diamine, dianhydride monomer and polyamic acid may bedissolved, but an example thereof may be an aprotic polar solvent.

Non-limiting examples of the aprotic polar solvent include amide-basedsolvents such as N,N′-dimethylformamide (DMF) and N,N′-dimethylacetamide(DMAc), phenol-based solvents such as p-chlorophenol, ando-chlorophenol, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL),and diglyme, which may be used alone or in combination of two or more.

In some cases, an auxiliary solvent such as toluene, tetrahydrofuran,acetone, methyl ethyl ketone, methanol, ethanol, and water may be usedto adjust the solubility of the polyamic acid.

In one example, organic solvents that may be particularly preferablyused in the preparation of the polyamic acid solution according to thepresent disclosure may be N,N′-dimethylformamide andN,N′-dimethylacetamide which are amide-based solvents.

The polyamic acid of the polyamic acid solution thus prepared may have aweight average molecular weight of 150,000 g/mole or more to 1,000,000g/mole or less, specifically 260,000 g/mole or more to 700,000 g/mole orless, and more specifically 280,000 g/mole or more to 500,000 g/mole orless.

The polyamic acid having such a weight average molecular weight may bepreferable for manufacturing a polyimide film having more excellent heatresistance and mechanical properties.

In general, since the weight average molecular weight of the polyamicacid may be proportional to viscosity of the polyamic acid solutioncontaining the polyamic acid and an organic solvent, the weight averagemolecular weight of the polyamic acid may be controlled within the aboverange by adjusting the viscosity.

This is because the viscosity of the polyamic acid solution isproportional to the content of a polyamic acid solid, specifically, thetotal amount of the dianhydride monomer and the diamine monomer used ina polymerization reaction. However, the weight average molecular weightdoes not represent a one-dimensional linear proportional relationshipwith the viscosity, but is proportional in the form of a log function.

That is, while the range in which the weight average molecular weightmay be increased even if the viscosity is increased in order to obtain apolyamic acid with a higher weight average molecular weight is limited,if the viscosity is excessively high, when the precursor composition isdischarged through a die in a film forming process of the polyimidefilm, a processability problem may be caused due to an increase inpressure inside the die.

Accordingly, the polyamic acid solution according to the presentdisclosure may contain 15% to 20% by weight of a polyamic acid solid and80% to 85% by weight of an organic solvent. In this case, the viscositymay be 90,000 cP or more to 350,000 cP or less, specifically 100,000 cPor more to 300,000 cP. Viscosity is measured at room temperature at ashear rate of 1 (1/sec). Within this viscosity range, the weight averagemolecular weight of the polyamic acid may fall within the above range,and the precursor composition may not cause problems in the film formingprocess described above.

The step of preparing a precursor composition by mixing inorganicfillers with the polyamic acid solution may include: milling orultrasonically dispersing a mixture of inorganic fillers and an organicsolvent, and mixing the mixture with the polyamic acid solution toprepare a precursor composition; or milling a mixture of inorganicfillers and an organic solvent in a state mixed with the polyamic acidsolution to prepare a precursor composition.

For the milling, the use of a bead milling method, without limitation,may be considered. The bead milling is advantageous for dispersionbecause the mixture may be effectively stirred even when the flow rateof the mixture is low. However, it should be understood that this isonly an example to aid in the implementation of the present disclosure.

In the step of forming a film on a support using the precursorcomposition and performing imidization to form a polyimide film, athermal imidization method, a chemical imidization method, or acomposite imidization method in which the thermal imidization method andthe chemical imidization method are used in combination may be used.

This will be described in more detail through the following non-limitingexamples.

<Thermal Imidization Method>

The thermal imidization method is a method of inducing an imidizationreaction with a heat source such as hot air or an infrared dryer,excluding a chemical catalyst, and may include:

drying the precursor composition to form a gel film; and

heat-treating the gel film to obtain a polyimide film;

Here, the gel film may be understood as a film intermediate havingself-supporting properties in an intermediate step for conversion frompolyamic acid to polyimide.

In the process of forming the gel film, the precursor composition may becast in a film form on a support such as a glass plate, an aluminumfoil, an endless stainless belt, or a stainless drum, and then theprecursor composition on the support may be dried at a variabletemperature in the range of 50° C. to 200° C., specifically 80° C. to200° C.

Accordingly, the precursor composition may be partially cured and/ordried to form a gel film. Then, peeling may be performed from thesupport to obtain a gel film

In some cases, a process of stretching the gel film may be performed inorder to adjust a thickness and a size of a polyimide film obtained in asubsequent heat treatment process and improve orientation of thepolyimide film, and stretching may be performed in at least one of amachine direction (MD) and a transverse direction (TD) with respect tothe machine direction.

The gel film thus obtained is fixed to a tenter, heat-treated at avariable temperature in the range of 50° C. to 650° C., specifically150° C. to 600° C. to remove water, residual solvents, etc., remainingin the gel film, and then almost all remaining amic acid groups areimidized to obtain a polyimide film of the present disclosure.

In some cases, the polyimide film as described above may be furthercured by heating and finishing the film at a temperature of 400° C. to650° C. for 5 seconds to 400 seconds, and the curing may be performedunder a predetermined tension in order to alleviate internal stress thatmay remain in the obtained polyimide film.

<Chemical Imidization Method>

The chemical imidization method is a method of promoting imidization ofthe amic acid group by adding a dehydrating agent and/or an imidizingagent to the precursor composition.

Here, “dehydrating agent” refers to a substance that promotes a ringclosure reaction through a dehydration action on polyamic acid.Non-limiting examples thereof include aliphatic acid anhydride, aromaticacid anhydride, N,N′-dialkylcarbodiimide, halogenated lower aliphatic,halogenated lower fatty acid anhydride, aryl phosphonic dihalide, andthionyl halide, etc. Among these, aliphatic acid anhydride may bedesirable in terms of availability and cost. Non-limiting examplesthereof include acetic anhydride (AA), propionic acid anhydride, andlactic acid anhydride. etc., and these may be used alone or incombination of two or more.

In addition, an “imidizing agent” refers to a substance having an effectof promoting a ring closure reaction with respect to polyamic acid, andmay be, for example, an imine-based component such as an aliphatictertiary amine, an aromatic tertiary amine, and a heterocyclic tertiaryamine. Among these, a heterocyclic tertiary amine may be desirable interms of reactivity as a catalyst. Non-limiting examples of theheterocyclic tertiary amine include quinoline, isoquinoline, β-picoline(BP), pyridine, etc., and these may be used alone or in combination oftwo or more.

The amount of the dehydrating agent added is preferably in the range of0.5 mol to 5 mol, and particularly preferably in the range of 1.0 mol to4 mol, based on 1 mol of the amic acid group in the polyamic acid. Inaddition, the amount of the imidizing agent added is preferably in therange of 0.05 mol to 2 mol, and particularly preferably in the range of0.2 mol to 1 mol, based on 1 mol of the amic acid group in the polyamicacid.

If the dehydrating agent and the imidizing agent are less than the aboverange, chemical imidization may be insufficient, cracks may be formed inthe polyimide film to be manufactured, and a mechanical strength of thefilm may also be reduced. In addition, if the amount of the dehydratingagent and the imidizing agent added exceeds the above range, imidizationmay proceed excessively quickly. In this case, it is difficult to becast in the film form or the manufactured polyimide film may exhibitbrittle properties, which is not preferable.

<Complex Imidization Method>

In connection with the above chemical imidization method, a compositeimidization method in which a thermal imidization method is additionallyperformed, may be used for the manufacture of the polyimide film.

Specifically, the composite imidization method may include: a chemicalimidization process of adding a dehydrating agent and/or an imidizingagent to the precursor composition at low temperature; and a thermalimidization process of drying the precursor composition to form a gelfilm and heat-treating the gel film.

During the chemical imidization process, the types and amounts of thedehydrating agent and the imidizing agent added may be appropriatelyselected as described in the above chemical imidization method.

In the process of forming the gel film, the precursor compositioncontaining the dehydrating agent and the imidizing agent is cast in afilm form on a support such as a glass plate, an aluminum foil, anendless stainless belt, or a stainless drum, and then the precursorcomposition on the support is dried at a variable temperature in therange of 50° C. to 200° C., specifically 80° C. to 200° C. In such aprocess, the dehydrating agent and/or the imidizing agent may act as acatalyst to rapidly convert an amic acid group into an imide group.

In some cases, a process of stretching the gel film may be performed inorder to adjust a thickness and a size of a polyimide film obtained in asubsequent heat treatment process and improve orientation of thepolyimide film, and stretching may be performed in at least one of amachine direction (MD) and a transverse direction (TD) with respect tothe machine direction.

The volatile content of the gel film may be applied as described in thethermal imidization method as described above.

The gel film thus obtained is fixed to a tenter, heat-treated at avariable temperature in the range of 50° C. to 650° C., specifically150° C. to 600° C. to remove water, catalysts, residual solvents, etc.,remaining in the gel film, and then almost all remaining amic acidgroups are imidized, thereby obtaining a polyimide film of the presentdisclosure. Even in such a heat treatment process, the dehydrating agentand/or the imidizing agent may act as a catalyst to rapidly convert theamic acid group into the imide group, thereby enabling theimplementation of a high imidization rate.

In some cases, the polyimide film as described above may be furthercured by heating and finishing the film at a temperature of 400° C. to650° C. for 5 seconds to 400 seconds, and the curing may be performedunder a predetermined tension in order to alleviate internal stress thatmay remain in the obtained polyimide film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph obtained by photographing a surface of apolyimide film according to Example 1.

FIG. 2 is a photograph obtained by photographing a surface of apolyimide film according to Comparative Example 6.

MODES OF THE INVENTION

Hereinafter, the action and effect of the present disclosure will bedescribed in more detail through specific examples of the presentdisclosure. However, these examples are only presented as examples ofthe invention, and the scope of the invention is not determined by theseexamples.

Example 1 Preparation Example 1-1 Preparation of a Precursor Composition

To a 1.0 L reactor was added 515.75 g of dimethylformamide (DMF) as anorganic solvent under a nitrogen atmosphere. After setting a temperatureto 25° C., 44.27 g of ODA was added as a diamine monomer, followed bystirring for about 30 minutes to confirm that the monomer was dissolved.Thereafter, 46.78 g of PMDA were added as a dianhydride monomer, andfinally, the final dose was adjusted and added so that the viscositybecame 100,000 cP to 150,000 cP to prepare a polyamic acid solution.

Thereafter, a precursor composition was prepared by mixing inorganicfillers including a first filler group and a second filler group havingthe following characteristics in a polyamic acid solution in an amountof 0.15% based on the content of the polyamic acid solid:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.1 μm, D90 of 3.0 μm, 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.5 μm, 30% by        weight based on the total weight of the inorganic fillers.

Preparation Example 1-2 Manufacture of Polyimide Film

To 100 g of the precursor composition prepared in Preparation Example1-1 were added 3.0 g of isoquinoline (IQ), 20.8 g of acetic anhydride(AA), and 16.2 g of DMF as a catalyst, the resulting mixture wasuniformly mixed and cast on a SUS plate (100SA, Sandvik) at 470 μm usinga doctor blade, and dried at a temperature range of 100° C. to 200° C.

Then, the film was peeled off from the SUS plate, fixed to a pin frame,and transferred to a high-temperature tenter.

The film was heated from 200° C. to 600° C. in the high-temperaturetenter, cooled at 25° C., and separated from the pin frame to obtain apolyimide film having a width*a length of 1 m*1 m and a thickness of 50μm.

Example 2

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2.7 μm, D10 of 1.5 μm, D90 of 4.1 μm, and 70%        by weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1.7 μm, D10 of 1.2 μm, D90 of 2.5 μm, and 30%        by weight based on the total weight of the inorganic fillers.

Example 3

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2.2 μm, D10 of 1.3 μm, D90 of 3.3 μm, and 70%        by weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1.3 μm, D10 of 0.9 μm, D90 of 1.9 μm, and 30%        by weight based on the total weight of the inorganic fillers.

Example 4

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2.2 μm, D10 of 1.3 μm, D90 of 3.3 μm, and 80%        by weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1.3 μm, D10 of 0.9 μm, D90 of 1.9 μm, and 20%        by weight based on the total weight of the inorganic fillers.

Example 5

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group, asecond filler group, and a third filler group having the followingcharacteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.1 μm, D90 of 3.0 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.5 μm, and 20% by        weight based on the total weight of the inorganic fillers;    -   Third filler group: Spherical silica having an average particle        diameter (D50) of 0.3 μm, D10 of 0.2 μm, D90 of 0.42 μm, and 10%        by weight based on the total weight of the inorganic fillers.

Example 6

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group, asecond filler group, and a third filler group having the followingcharacteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2.7 μm, D10 of 1.5 μm, D90 of 4.1 μm, and 70%        by weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1.7 μm, D10 of 1.2 μm, D90 of 2.5 μm, and 20%        by weight based on the total weight of the inorganic fillers;    -   Third filler group: Spherical silica having an average particle        diameter (D50) of 0.6 μm, D10 of 0.4 μm, D90 of 0.9 μm, and 10%        by weight based on the total weight of the inorganic fillers.

Comparative Example 1

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Calcium phosphate having an average particle        diameter (D50) of 2 μm, D10 of 0.7 μm, D90 of 5.3 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Barium sulfate having an average particle        diameter (D50) of 1 μm, D10 of 0.4 μm, D90 of 2.3 μm, and 30% by        weight based on the total weight of the inorganic fillers.

Comparative Example 2

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a single filler grouphaving the following characteristics:

-   -   Filler group: Calcium phosphate having an average particle        diameter (D50) of 2 μm, D10 of 0.7 μm, D90 of 5.3 μm, and 100%        by weight based on the total weight of the inorganic fillers.

Comparative Example 3

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 3 μm, D10 of 1.7 μm, D90 of 4.7 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.5 μm, and 30% by        weight based on the total weight of the inorganic fillers.

Comparative Example 4

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.1 μm, D90 of 3.0 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 0.6 μm, D10 of 0.4 μm, D90 of 0.9 μm, and 30%        by weight based on the total weight of the inorganic fillers.

Comparative Example 5

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.1 μm, D90 of 3.0 μm, and 50% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.5 μm, and 50% by        weight based on the total weight of the inorganic fillers.

Comparative Example 6

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 0.8 μm, D90 of 3.5 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.3 μm, D90 of 1.8 μm, and 30% by        weight based on the total weight of the inorganic fillers.

Comparative Example 7

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group and asecond filler group having the following characteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.5 μm, D90 of 2.6 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.3 μm, and 30% by        weight based on the total weight of the inorganic fillers.

Comparative Example 8

A polyimide film was manufactured in the same manner as in Example 1,except for using inorganic fillers including a first filler group, asecond filler group, and a third filler group having the followingcharacteristics:

-   -   First filler group: Spherical silica having an average particle        diameter (D50) of 2 μm, D10 of 1.1 μm, D90 of 3.0 μm, and 70% by        weight based on the total weight of the inorganic fillers;    -   Second filler group: Spherical silica having an average particle        diameter (D50) of 1 μm, D10 of 0.7 μm, D90 of 1.5 μm, and 10% by        weight based on the total weight of the inorganic fillers;    -   Third filler group: Spherical silica having an average particle        diameter (D50) of 0.3 μm, D10 of 0.2 μm, D90 of 0.4 μm, and 20%        by weight based on the total weight of the inorganic fillers.

The inorganic fillers used in the above Examples and ComparativeExamples are briefly summarized in Table 1 below.

TABLE 1 Type of First Second Third inorganic filler filler group fillergroup filler group Characteristics Content D50 D10 D90 Content D50 D10D90 Content D50 D10 D90 Example 1 Spherical 70 2 1.1 3.0 30 1 0.7 1.5 —— — — silica Example 2 Spherical 70 2.7 1.5 4.1 30 1.7 1.2 2.5 — — — —silica Example 3 Spherical 70 2.2 1.3 3.3 30 1.3 0.9 1.9 — — — — silicaExample 4 Spherical 80 2.2 1.3 3.3 20 1.3 0.9 1.9 — — — — silica Example5 Spherical 70 2 1.1 3.0 20 1 0.7 1.5 10 0.3 0.2  0.42 silica Example 6Spherical 70 2.7 1.5 4.1 20 1.7 1.2 2.5 10 0.6 0.4 0.9 silica Comp.Calcium 70 2 0.7 5.3 30 1 0.4 2.3 — — — — Example 1 phosphate/ Bariumsulfate Comp. Calcium 100 2 0.7 5.3 — — — — — — — — Example 2 phosphateComp. Spherical 70 3 1.7 4.7 30 1 0.7 1.5 — — — — Example 3 silica Comp.Spherical 70 2 1.1 3.0 30 0.6 0.4 0.9 — — — — Example 4 silica Comp.Spherical 50 2 1.1 3.0 50 1 0.7 1.5 — — — — Example 5 silica Comp.Spherical 70 2 0.8 3.5 30 1 0.3 1.8 — — — — Example 6 silica Comp.Spherical 70 2 1.5 2.6 30 1 0.7 1.3 — — — — Example 7 silica Comp.Spherical 70 2 1.1 3.0 10 1 0.7 1.5 20 0.3 0.2 0.4 Example 8 silica

Whether or not the fillers used in Examples 1 to 6 and ComparativeExamples 1 to 8 satisfy the following relational expression 1 issummarized in Table 2 below:

0.7≤(D90−D10)/(D50)≤1.2  (1).

TABLE 2 First filler group Second filler group Third filler groupWhether or Whether or Whether or Relational not Relational Relationalnot Relational Relational not Relational expression expression 1expression expression 1 expression expression 1 1 is satisfied 1 issatisfied 1 is satisfied Example 1 0.95 ◯ 0.80 ◯ — — Example 2 0.96 ◯0.76 ◯ — — Example 3 0.91 ◯ 0.77 ◯ — — Example 4 0.91 ◯ 0.77 ◯ — —Example 5 0.95 ◯ 0.80 ◯ 0.73 ◯ Example 6 0.96 ◯ 0.76 ◯ 0.83 ◯ Comp. 2.30X 1.90 X — — Example 1 — — Comp. 2.30 X — — — — Example 2 Comp. 1.00 ◯0.80 ◯ — — Example 3 Comp. 0.95 ◯ 0.83 ◯ — — Example 4 Comp. 0.95 ◯ 0.80◯ — — Example 5 Comp. 1.35 X 1.50 X — — Example 6 Comp. 0.55 X 0.60 X —— Example 7 Comp. 0.95 ◯ 0.80 ◯ 0.67 X Example 8

Experimental Example 2: Properties Evaluation of Polyimide Film

1) Average roughness evaluation: An average roughness of each polyimidefilm was measured using a 1S01997 method under the measurementconditions of cut off of 0.25 mm, measurement speed of 0.1 mm/sec, andmeasurement length of 3 mm per time, and the average value obtained bymeasuring five times was used. Here, the surface for which the averageroughness was measured was an air surface of the polyimide film (theopposite surface of the surface in contact with the plate or thetenter). The above average roughness results are shown in Table 3 below.

2) Surface defect evaluation: The surfaces of the polyimide filmsmanufactured in the Examples and the Comparative Examples were observedwith a microscope to check the number of defects having a long diameterof 30 um or more per unit area of 1 m*1 m, and the results are shown inTable 3 and FIG. 1 (Example 1), and FIG. 2 (Comparative Example 6).

3) Haze evaluation: A haze value was measured on the A light sourceusing a HM150 model.

4) Transmittance evaluation: Transmittance was measured by a methodpresented in ASTM D1003 in the visible light region using aColorQuesetXE model available from HunterLab, com.

However, the transmittance is a relative value to 1, which is atheoretical maximum transmittance in an arbitrary object, and is shownin Table 3 below.

TABLE 3 Average roughness (Number of) (nm) Surface defects HazeTransmittance Example 1 26.1 2 8.1 0.55 Example 2 39.1 3 11.9 0.43Example 3 30.3 0 9.4 0.51 Example 4 30.7 0 9.0 0.50 Example 5 21.3 1 7.50.59 Example 6 34.7 6 11.0 0.45 Comp. Example 1 15.3 53 8.0 0.43 Comp.Example 2 18.5 32 7.3 0.51 Comp. Example 3 45.3 25 10.5 0.47 Comp.Example 4 25.8 18 14.1 0.35 Comp. Example 5 29.2 22 14.8 0.32 Comp.Example 6 42.4 31 8.4 0.47 Comp. Example 7 29.7 13 13.8 0.35 Comp.Example 8 28.1 29 13.3 0.38

From the results in Table 3, the polyimide films of all Examples inwhich the relational expression 1 is satisfied, D50, D90, and D10 fallwithin the range of the present disclosure, and the content of eachfiller group is also within the scope of the present disclosure, showedan average roughness of 20 nm or more, a haze of 12 or less, atransmittance of 0.4 or more, and an excellent smoothness.

In addition, it can be seen that the polyimide film of Examples had nosurface defects (protrusions). For surface defects, it can be confirmedthat the polyimide film has a smooth surface with reference to FIG. 1obtained by photographing the surface of the polyimide film according toExample 1.

Meanwhile, it can be seen that in the Comparative Examples where atleast one of various factors according to the present disclosure,specifically, a filler group type, a content, a particle diameter, andrelational expression 1 is unsatisfactory, at least one of averageroughness, haze, transmittance, and smoothness is poor. It should benoted that from the results of these Comparative Examples, the averageroughness, transmittance, and smoothness, which are difficult to becompatible with each other, may be compatible at an appropriate levelwhen the experiment is carried out according to the present disclosure.

In addition, as described above, the Comparative Examples deviating fromthe present disclosure include a plurality of surface defects, forexample, as shown in FIG. 2, and thus include the conventional problemas it is.

Experimental Example 3: Modulus Evaluation of Polyimide Film

The moduli of the polyimide films of Examples were measured by a methodsuggested in ASTM D882 using an Instron 5564 model, and measurementresults are shown in Table 4.

TABLE 4 Modulus (GPa) Example 1 3.0 Example 2 2.7 Example 3 2.8 Example4 3.3 Example 5 3.4 Example 6 2.6

It can be seen from the results of Table 4 that the polyimide filmaccording to the present disclosure has a modulus of 3.5 GPa or less.

Although the above description has been made with reference to theembodiments of the present disclosure, a person of ordinary skill in thefield to which the present disclosure pertains will be able to makevarious applications and modifications within the scope of the presentdisclosure based on the above mentioned.

INDUSTRIAL APPLICABILITY

The present disclosure described in detail above the advantages of apolyimide film including inorganic fillers, specifically, a polyimidefilm that satisfies the specific relational expression 1 of the presentdisclosure and includes inorganic fillers consisting of a plurality offiller groups having different particle diameters.

In summary, the polyimide film of the present disclosure hassubstantially no protrusions due to filler aggregation, and may have anaverage roughness, smoothness, and transmittance at an appropriatelevel, which are difficult to be compatible with each other by fillergroups having different average particle diameters.

1. A polyimide film, comprising a base film made of polyimide, andinorganic fillers dispersed in the base film, wherein the polyimide filmhas a modulus of 3.5 GPa or less, the inorganic fillers include a firstfiller group having an average particle diameter (D50) falling withinthe range of 2 μm to 2.7 μm and a second filler group having an averageparticle diameter (D50) falling within the range of 1 μm to 1.7 μm, andeach of the first filler group and the second filler group satisfies thefollowing relational expression 1 for particle diameters:0.7≤(D90−D10)/D50≤1.2  (1).
 2. The polyimide film of claim 1, whereinthe first filler group is included in an amount of 60% to 80% by weightand the second filler group is included in an amount of 20% to 40% byweight, based on the total weight of the inorganic fillers.
 3. Thepolyimide film of claim 1, wherein the inorganic fillers further includea third filler group having an average particle diameter (D50) fallingwithin the range of 0.3 μm to 0.6 μm and satisfying the relationalexpression
 1. 4. The polyimide film of claim 3, wherein the third fillergroup is included in an amount of 5% by weight or more to less than 20%by weight, based on the total weight of the inorganic fillers.
 5. Thepolyimide film of claim 1, wherein the inorganic filler is one or moreselected from the group consisting of silica, calcium phosphate, calciumcarbonate, and barium sulfate.
 6. The polyimide film of claim 5, whereinthe inorganic filler is spherical silica.
 7. The polyimide film of claim1, wherein the inorganic filler is included in an amount of 0.05% to0.3% by weight, based on the total weight of the polyimide film.
 8. Thepolyimide film of claim 1, wherein the first filler group has D90 of 3.0μm to 4.1 μm and D10 of 1.0 μm to 1.6 μm, and the second filler grouphas D90 of 1.5 μm to 2.5 μm and D10 of 0.7 μm to 1.2 μm.
 9. Thepolyimide film of claim 3, wherein the third filler group has D90 of 0.4μm to 0.9 μm and D10 of 0.2 μm to 0.4 μm.
 10. The polyimide film ofclaim 1, wherein a haze of the polyimide film is 12 or less, an averageroughness of the polyimide film is 20 nm or more, and the number ofsurface defects having a long diameter of 30 um or more per unit area of1 m*1 m of the polyimide film is 10 or less.
 11. The polyimide film ofclaim 1, wherein the polyimide film satisfies the following relationalexpression 2:12 μm≤T*L≤40 μm  (2) wherein T is a thickness of the polyimide film andis 30 μm to 50 μm, and L is a transmittance of the polyimide film, is arelative value to 1 which is a theoretical maximum transmittance, and is0.4 to 0.6.
 12. The polyimide film of claim 1, wherein the polyimideforming the base film is derived from imidization of a polyamic acidformed by polymerization of a dianhydride monomer and a diamine monomer.13. The polyimide film of claim 12, wherein the dianhydride monomer ispyromellitic dianhydride (PMDA), and the diamine monomer is one or moreselected from the group consisting of 4,4′-diaminodiphenyl ether(4,4′-ODA), 3,4′-diaminodiphenyl ether (3,4′-ODA), p-methylenedianiline(p-MDA) and m-methylenedianiline (m-MDA).
 14. A method of manufacturingthe polyimide film of claim 1, the method comprising: polymerizing adianhydride monomer and a diamine monomer in an organic solvent toprepare a polyamic acid solution; mixing inorganic fillers with thepolyamic acid solution to prepare a precursor composition; and forming afilm on a support using the precursor composition and performingimidization to form the polyimide film.
 15. An electronic devicecomprising the polyimide film of claim 1 as at least one of an opticalfilm, an insulating film, and a protective film.
 16. The electronicdevice of claim 15, wherein the electronic device is a display device ora wearable instrument whose shape is variably deformed through at leastone selected from bending, curving, and rolling, and the polyimide filmis deformed together in response to the deformation of the electronicdevice.